Add AWS AppSyncEvent

[PankajRawat333]

Issue #, if available:
#1938

Description of changes:

• Added AWS AppSyncEvent to consume and process event directly on Lambda function.
• Added unit tests

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ashishdhingra]

@PankajRawat333 Thanks for the PR. Please refer type information from https://www.npmjs.com/package/@types/aws-lambda?activeTab=code. Source: https://github.com/aws-samples/cdk-typescript-appsync-lambda/blob/main/src/Resolver/src/resolver.ts#L24.

[PankajRawat333]

@ashishdhingra I have updated type according to above link.

[ashishdhingra]

@ashishdhingra I have updated type according to above link.

@PankajRawat333 Thanks for addressing comments for the PR. Discussed this PR with the team. @normj would have a high level look. Meanwhile, could you also please follow up with the Lambda team to get the schema details and data types for each field (since these are not documented in detail)? We would need to make sure to use the correct types for each field to avoid making any breaking changes in future for missed scenario.